The invention relates generally to injection molding systems, and more particularly to improved pressure bushings for coupling molten materials extrusion nozzles to hot tip systems and combinations thereof.
Hot tip systems are known and include generally one or more heated tips for supplying molten materials, usually molten plastics, to corresponding mold cavities. to Exemplary hot tip systems include the HPS Single and Multi-Tip Nozzle Standard and Special Systems, Types 97, 98 and 99, available from Ewikon N.A. Inc., Elgin, Ill. The molten material is supplied to the hot tip system by an extrusion nozzle of an injection molding machine. More particularly, the hot tip system, including the mold, is mounted and clamped in the injection molding machine between fixed and movable platens thereof. The extrusion nozzle is coupled to the hot tip system by a pressure bushing, which is mounted or otherwise securely fastened to the hot tip system. In operation, the extrusion nozzle is advanced toward and biased into seated engagement with the pressure bushing as molten material is supplied therefrom under pressure to the hot tip system. The force exerted by the extrusion nozzle on the pressure bushing varies depending on the type and rated clamping tonnage of the injection molding machine. The pressure at which the molten material is supplied from the extrusion nozzle to the hot runner system depends on the injection molding machine and hot tip system configurations.
In the past, injection molding machines were operated hydraulically, including operation of the movable platen, advancement and retraction of the extrusion nozzle, and extrusion of molten material therefrom. More recently, the hydraulic injection molding machines are being replaced in many applications by electric injection molding machines, which have several advantages over the hydraulic machines. Electric injection molding machines have, for example, substantially reduced power consumption and other operational cost savings some of which result from the elimination of hydraulic components. Electric machines are also not susceptible to drift, which plagues hydraulic machines, and provide generally more precise control over fluid pressure regulation and other systems operations, thereby providing more consistent molding performance and improved productivity.
Most hot tip systems were designed originally for use with hydraulic machines, and when used with electric machines have a tendency to eject molten material at high pressure from between the extrusion nozzle and the pressure bushing, a phenomenon referred to sometimes as blowback. Besides the obvious safety hazard blowback poses to personnel, it also adversely affects the supply of molten material to the hot tip system and the mold cavities by diverting the molten material supply and reducing supply pressure, thereby resulting in inconsistent molding performance.
Blowback of ejecta was not a significant problem with hydraulic injection molding machines because, in comparison to electric machines, hydraulic machines exert a relatively high force to bias the extrusion nozzle into seated engagement with the pressure bushing as molten material is supplied therefrom to the hot tip system.
The present invention is drawn toward advancements in the art of injection molding systems, and more particularly to novel pressure bushings for coupling injection molding machines to hot tip systems and combinations thereof.
The inventors of the present invention recognized that molten material ejecta may be eliminated or at least substantially reduced by appropriately modifying the pressure bushing by generally reducing the size of the molten material passage therethrough. The pressure bushing of the HPS Single and Multi-Tip Nozzle Standard and Special Systems discussed above, for example, have a passage diameter of approximately 0.475 inches and an axial dimension of approximately 0.125 inches. Other known pressure bushings have passage diameters of approximately 0.250 inches. These prior art pressure bushings, and more particularly the dimensions of the molten material passages therethrough, were designed for hydraulic molding machines, and when used with electric machines exhibit blowback of ejecta, which is undesirable.
Hot tip manufacturers and others have expressed mistaken concerns that reducing the size of the pressure bushing passage would unduly increase molten material supply pressure, and would give rise to an excessive pressure drop in the hot tip system, thereby adversely affecting molding performance. It was also believed, incorrectly, that molten material in the pressure bushing passage would have a tendency to form a hardened plug, a phenomenon referred to sometimes as freeze-off, especially upon cessation of the molten material supply and upon retraction of the extrusion nozzle away from the pressure bushing, and that the hardened plug would obstruct the supply of molten material to the tips of the hot tip system and possibly damage an internal heater tube thereof upon re-establishing the molten material supply. These concerns however proved erroneous.
It is an object of the invention to provide novel injection molding systems that overcome problems in the prior art, and novel injection molding systems that are economical to manufacture and operate.
It is also an object of the invention to provide novel injection molding systems that provide more consistent molding performance.
It is another object of the invention to provide novel injection molding systems that eliminate or at least substantially reduce blowback of ejecta from a coupling between injection molding machines, particularly electric injection molding machines, and hot tip systems.
It is a further object of the invention to provide novel injection molding systems with improved pressure bushings for coupling injection molding machines and hot tip systems, and improved pressure bushings that are retrofittable in existing injection molding systems.
A more particular object of the invention is to provide novel injection molding systems including an injection molding machine, especially an electric injection molding machine, coupleable to a hot tip system having an improved pressure bushing with a generally reduced molten material passage therethrough that eliminates or at least substantially reduces ejecta from the coupling between an extrusion nozzle of the molding machine and the pressure bushing without freeze-out.
These and other objects, aspects, features and advantages of the present invention will become more fully apparent upon careful consideration of the following Detailed Description of the Invention and the accompanying Drawings, which may be disproportionate for ease of understanding, wherein like structure and steps are referenced generally by corresponding numerals and indicators.